Ilene J. Busch‐Vishniac

Noise levels in Johns Hopkins Hospital

This article presents the results of a noise survey at Johns Hopkins Hospital in Baltimore, MD. Results include equivalent sound pressure levels (L(eq)) as a function of location, frequency, and time of day. At all locations and all times of day, the L(eq) indicate that a serious problem exists. No location is in compliance with current World Health Organization Guidelines, and a review of objective data indicates that this is true of hospitals throughout the world. Average equivalent sound levels are in the 50-60 dB(A) range for 1 min, 1/2, and 24 h averaging time periods. The spectra are generally flat over the 63-2000 Hz octave bands, with higher sound levels at lower frequencies, and a gradual roll off above 2000 Hz. Many units exhibit little if any reduction of sound levels in the nighttime. Data gathered at various hospitals over the last 45 years indicate a trend of increasing noise levels during daytime and nighttime hours. The implications of these results are significant for patients, visitors, and hospital staff.

Feasibility of micro power supplies for MEMS

Most microelectromechanical systems (MEMS) designed today use macroscopic power supplies, thereby placing limits on the functionality of MEMS in many applications. An alternative to this approach is to design MEMS with integral microscopic distributed power supplies. This paper examines the feasibility of creating micro power supplies by considering three functions common to MEMS power systems: (1) capture energy; (2) store energy; and (3) drive actuation, of these, only the capture energy function is highly dependent on the specific application. For each of the three functions, a table is presented which compares various means of performing the function. This information makes it possible to determine what design alternatives are feasible for the creation of a micro power supply for any specific application of MEMS. We use smart bearings with active surface features as an example application and develop a design for a micro power supply suitable for this work.

Noise in the operating rooms of Johns Hopkins Hospital

Very little reliable information exists on the sound levels present in an operating room environment. To remedy this situation, sound pressure levels of the operating rooms in Johns Hopkins Hospital were monitored before, during, and after operations. The data were analyzed to determine background sound levels, average equivalent sound levels L(eq), frequency distribution, and peak sound pressure levels L(peak). Each surgery was matched to the period of noise it produced permitting the association of sound levels with particular types of surgeries and the determination of various sound measures for classes of surgery (e.g., orthopedic, neurological, etc.). Averaging over many surgeries, orthopedic surgery was found to have the highest L(eq) at approximately 66 dB(A). Neurosurgery, urology, cardiology, and gastrointestinal surgery followed closely, ranging from 62 to 65 dB(A). By considering the L(peak) along with the L(eq) values, a pattern emerges for the various surgical divisions. Gastrointestinal and thoracic surgery are relatively quiet among the surgical divisions. Neurosurgery and orthopedics have sustained high sound levels. Cardiology surgery has a more moderate average sound level but includes brief periods of extremely high peak sound levels. For neurosurgery and orthopedic surgery, peak levels exceeded 100 dB over 40% of the time. The highest peak levels routinely seen during surgery were well in excess of 120 dB.

The case for magnetically driven microactuators

Abstract There has been a growing interest in microactuation, which we define as the ability to achieve motions with micron-level precision, and in microfabricated actuators, which we define as actuators which are themselves micron scale in size. Recent articles on microfabricated actuators have suggested that electrostatic approaches are more favorable than magnetic approaches. This article revisits these issues from the perspective of microactuation with application to microfabricated actuators. We show that magnetically generated forces can be made much larger than electrostatic forces even for 1 μm air gaps, that efficiency arguments are moot unless microfabricated actuators shrink further in size (in which case heat dissipation is a problem), and that the benefits of integration of electronics with a microactuator are questionable. We also show, by direct comparison of a magnetic and an electrostatic microfabricated actuator, that magnetic approaches which are wholly compatible with microelectronics fabrication can produce forces comparable to those from electrostatic approaches. From these arguments we conclude that the case for magnetic microactuation and magnetically driven microfabricated actuators is compelling, and that the advantages of microfabrication of actuators are not clear.

Wave-scattering approaches to conservation and causality

Abstract System description requires specification of two things: the elements and their interconnections. In the customary circuit approach these attributes are treated distinctly, but in the wave-scatter approach they are treated uniformly. This permits direct representation of elements such as transformers and gyrators. All physical system interaction occurs through power interchange, represented here using a signal duplex over the connecting bonds and through the element ports. Causality is thus intrinsic and conservation is imposed via unitarity and orthogonality of the element scattering matrices. This representation is suitable for linear and nonlinear systems.

Quieting Weinberg 5C: A case study in hospital noise control

Weinberg 5C of Johns Hopkins Hospital is a very noisy hematological cancer unit in a relatively new building of a large medical campus. Because of the requirements for dealing with immuno-suppressed patients, options for introducing sound absorbing materials are limited. In this article, a case study of noise control in a hospital, the sound environment in the unit before treatment is described, the chosen noise control approach of adding custom-made sound absorbing panels is presented, and the impact of the noise control installation is discussed. The treatment of Weinberg 5C involved creating sound absorbing panels of 2-in.-thick fiberglass wrapped in an anti-bacterial fabric. Wallpaper paste was used to hold the fabric to the backing of the fiberglass. Installation of these panels on the ceiling and high on corridor walls had a dramatic effect. The noise on the unit (as measured by the equivalent sound pressure level) was immediately reduced by 5 dB(A) and the reverberation time dropped by a factor of over 2. Further, this drop in background noise and reverberation time understates the dramatic impact of the change. Surveys of staff and patients before and after the treatment indicated a change from viewing the unit as very noisy to a view of the unit as relatively quiet.

Noise in the adult emergency department of Johns Hopkins Hospital

While hospitals are generally noisy environments, nowhere is the pandemonium greater than in an emergency department, where there is constant flow of patients, doctors, nurses, and moving equipment. In this noise study we collected 24 h measurements throughout the adult emergency department of Johns Hopkins Hospital, the top ranked hospital in the U.S. for 16 years running. The equivalent sound pressure level (Leq) throughout the emergency department is about 5 dB(A) higher than that measured previously at a variety of in-patient units of the same hospital. Within the emergency department the triage area at the entrance to the department has the highest Leq, ranging from 65 to 73 dB(A). Sound levels in the emergency department are sufficiently high [on average between 61 and 69 dB(A)] to raise concerns regarding the communication of speech without errors--an important issue everywhere in a hospital and a critical issue in emergency departments because doctors and nurses frequently need to work at an urgent pace and to rely on oral communication.

Position dependence of the transient response of a position-sensitive detector under periodic pulsed light modulation

A model based on sinusoidal steady-state analysis is developed for the position-sensitive detector (PSD), which is approximated as a distributed RC transmission line. This model is used to study the output response of the lateral effect PSD (i) when only one pulse-modulated light beam is incident and (ii) when two light beams of different wavelengths, with one beam modulated at a frequency f and the other beam modulated at a frequency 2f, are incident at the same time. The simulation shows, and experiments confirm, that the transient response of the PSD consists of a position-dependent dead time (time for the output current to sense the change in the induced photocurrent) and a position-independent exponential rise decay time. For the application of resolving the positions of two or more pulsed-modulated light spots, it is shown that there is a position-dependent upper limit on the usable modulation frequency. With the per-unit-length values chosen for the sheet resistance as R=315 Omega /mm and the junction capacitance as C=330 pF/mm, the modulation frequency limit is determined to be 20 kHz. >

Position detection of multiple light beams using phase detection

Earlier work on lateral-effect position-sensitive detectors (PSD) has used an amplitude detection signal-processing scheme to determine the position of the centroid of the incident light beam on the PSD surface. In this work we introduce a phase detection method of position measurement which is based on detecting the phase difference between the sinusoidal currents flowing through the metal electrodes. A distributed transmission line model for the PSD and a one-pole model for the transimpedance preamplifier are used in the analysis of the sensor. Experimental results are presented and are found to be in close agreement with simulation results. It is seen that the spatial resolution is proportional to the modulation frequency. With a light modulation frequency of 50 kHz and the introduction of frequency multiplication (/spl times/8) after the transimpedance preamplifier, a spatial resolution of 2 /spl mu/m is demonstrated. For application in multi-degree-of-freedom position sensors, we demonstrate the simultaneous detection of centroids of multiple light beams using frequency division multiplexing. Application of the phase method of position detection to a two dimensional PSD shows a maximum deviation from linearity of 1% over the working range of the PSD. >

Thermoacoustic radiation of sound by a moving laser source

The generation of sound by a moving laser source is investigated both theoretically and experimentally. The analysis is restricted to sound waves generated exclusively through the thermal mechanism. The model is based on the impulse response of a thermoacoustic source as described in a previous paper [J. Acoust. Soc. Am. 78, 2074–2082 (1985)]. The results presented here include pressure waveforms, directivity patterns, sound level dependence on source velocity, and spreading curves for subsonic, transonic, and supersonic source velocities. In general, experimental results are in good agreement with theoretical predictions.